Separation of ammonium salts from their mixtures with other salts



atente Nov. 17, 1936 ITED STATES PATENT OFFICE SEPARATION OF ADIMONIUM SALTS FROM THEIR DIDITUBIES WITH OTHER SALTS No Drawing. Application December 18, 1934, Serial No. 758,144. In France January 13,

6 Claims.

It has been already proposed to separate ammonium chloride from nitrates or other alkaline salts by a froth flotation process similar to those utilized in modern ore concentration installations, according to which a gas such as air in a finelydivided state is added to a suitable saline solution containing in suspension the mixture of salts to be separated, so as to form froth containing the ammonium chloride which rises to the surface, while the other constituents of the saline mixture remain in the solution in which they are caused to settle.

It is known that the selective attachment of the air bubbles to the ammonium chloride of the saline mixture for causing flotation of the said salt, necessitates the'use in small quantities of certain products called flotation agents, the essential function of which is to produce such surface conditions that the gas bubbles can become attached in a stable manner and in suflicient quantity to the ammonium chloride.

This process of salt separation has numerous disadvantages which consist chiefly in the dimculty of carrying it into practice, and more particularly in the necessity of a judicial introduction and of an exact amount of the flotation fluid (gas bubbles) and in the selective attachment of the latter to the ammonium chloride by means of intermediate products (flotation agents), the

introduction, amount and distribution of which require great attention.

The choice of the flotation agents is often a delicate matter owing to the fact that it is necessary to take into account not only the salts to be separated, but also the composition of the suspension liquids which are saline solutions containing various salts instead of being almost pure water as in the flotation of ore froth. Owing to this limitation of the number of possible agents, the-field of application of froth flotation to the separation of salts is greatly reduced; in fact the only salt, the flotation of which could be carried out up to the present, is ammonium chloride.

The agents are generally expensive and their diflicult recovery is liable to lead to considerable losses.

Moreover owing to the formation of voluminous froth which is characteristic of the froth flotation process, it is necessary to use apparatus of large dimensions and therefore expensive, for the flotation proper, for the destruction of the froth and for the recovery of the ammonium chloride floated.

All these disadvantages are avoided according to the present invention by using in place of air, products which are liquid at the working temperatures, more particularly oils, as flotation means to be attached to the salts to be floated; the formation of froth and the use of flotation agents being eliminated.

The present invention relates to a process of separation by flotation of ammonium salts from their mixtures with one or more other salts, comprising substantially three stages:

I. The homogeneous admixture of the saline mixture to be separated, with a suspension liquid and a flotation liquid.

11. The separation of the floated mass, substantially constituted 'by the ammonium salts of the mixture, and the flotation liquid.

III. The treatment of the mass for the purpose of obtaining the ammonium salt or salts floated and for recovering the flotation liquid which is re- Finally the invention comprises as new industrial products, the separated salts which still contain small amounts of the flotation liquids, the latter having been suitably chosen to impart to the said salts special properties.

The admixture of the suspension and flotation liquids and of the saline mixture as well as the homogenization of the whole may be effected in any suitable manner (kneading, agitation, pumps, injectors, funnels, etc.) either in an apparatus for this purpose, or in the apparatus in which the flotation proper is effected.

The choice of the suspension liquids is determined by the following factors: Their density must be less than that of each of the non-ammoniacal salts of the mixture of salts to be separated. Preferably they should not modify the composition of the said mixture by physical or chemical action. Solutions saturated with respect to all the constituents of the saline mixture 40 at the working temperatures are more particularly suitable.

The flotation liquids according to the invention comprise any combinations or mixtures which are liquid at the working temperatures, have densities less than that of the suspension liquid, are not miscible in all proportions with the suspension liquid, change but little under the conditions of use, and which can be'attached under certain conditions exclusively, or almost exclusively, to the ammonium salt or salts of the saline 1 mixture in such quantities as to produce the formation of pulp containing the ammonium salt or salts; lighter than the suspension liquid, and stable during the flotation, but readily capable of breaking down into their constituents after isolation by flotation.

Among the flotation liquids which fulfill the conditions above set forth, are more particularly mentioned mineral, animal or vegetable oils. The oils most suitable are gas-oil, parafflne oil, arachidic oil, olive oil, castor oil and linseed oil.

It has been found that the formation of the Pulp hereinbefore defined and the stability of the same during the flotation, depend to a great extent on the reaction, that is to say on the acidity, neutrality or alkalinity of the medium, which reaction itself can be easily influenced for instance by the hydrogen ion concentration, or pH value, of the suspension liquid.

According to the invention, with a given saline mixture and flotation liquid, the pH value of the flotation medium is therefore chosen in such a manner that the conditions of formation and the stability of the pulp should be optimum. For the same purpose may also be chosen flotation liquids in accordance with the saline mixture and the pH value of the suspension liquid if the said pH value is predetermined by certain operations which are to be carried out subsequently such as for instance the purification of the salts separated.

Tests have shown that it is particularly suitable for the separation of ammonium chloride and sodium nitrate to employ as a suspension agent the mother liquor, having served for the double decomposition of ammonium nitrate and sodium chloride, and containing at least 3 grams of free NH: per liter. If the degree of alkalinity is less the flotation of ammonium chloride is less easy. The flotation is practically impossible when there is less than 0.5 gram of free NH; per liter. On the contrary more than 3 grams of free NH: per liter may exist without danger. This is always true whether the flotation bodies are mineral, such as gas-oil, or vegetable, such as arachidic oil, or a mixture of vegetable and mineral compo-'- nents, for example a mixture of arachidic oil and gasoline.

On the contrary, if the separation of ammonium chloride from potassium nitrate is attempted it will be found that the flotation wheneflected with mineral oil, such as gas-oil, improves in proportion as the content of NH3 increases, then until this content exceeds 5 grams per liter at which point the flotation becomes less easy. By using a vegetable oil, such as arachidic oil alone or mixed with a mineral oil such as gasoline, the content of 5 grams of NI-I3 per liter may be exceeded without dimculties.

The separation of the floated pulp and for the salts deposited during the flotation can be carried out in the usual continuous or non-continuous decanting apparatus.

For breaking down the isolated pulp into its essential constituents, i. e., the ammonium salt or salts and the flotation liquid, well known means such as a centrifuge, injection of steam, etc. may be used. These means are however either oomphcated or expensive, and may not free completely the floated salts from the accompanying flotation liquid.

According to the present invention it is possible to obtain as complete a separation as may be desired of the floated salts and of the flotation liquid by arranging that the suspension liquid shall be carried away with the pulp during the isolation of the same. The pH value of the suspension liquid carried away, is thereupon modifled in such a manner as to render the pulp unstable. Owing to this operation during which it is advisable to agitate, there takes place an im= mediate formation of three clearly distinct stages: the ammonium salt or salts settle, and the flotation liquid collects on the surface of the suspension liquid. The ammonium salt or salts, the flotation liquid ready to be utilized again, and the suspension liquid, which can also be utilized again after a suitable treatment to restore the composition to its original form before the variation of its pH value, are thereupon separately collected by well known means.

It will be understood that a similar method of working renders possible the elimination from the deposit of non-ammoniacal salts obtained during the flotation, of any flotation liquid which may be contained therein.

In certain cases, more particularly when the salts separated are to be used as fertilizers, it may be very advantageous to allow a. portion of the flotation liquid to remain in contact with the separated salts whereby the latter will be coated in a very uniform manner.

This particularly simple, emcacious and inexpensive method of preparing products which are hygroscopic to a small degree only or not at all, which do not agglomerate when stored and are easy to handle or to spread, is comprised in the present invention as well as by way of new industrial products, the coated salts obtained in that-manner.

Example To 10 cubic meters of mother liquor containing:

there is added 800 kg. of NH4NO3 and 585 kg. NaCl and the mixture agitated for four hours at 25 C. after which it is cooled to 20 C.

' The mother liquor containing the crystals in suspension is passed by means of a centrifugal pump in a cylinder of a diameter of 1.50 meters, at the rate of liters per minute. At the intake of the pump ordinary commercial gas-oil is added at the rate of 100 liters per minute, and the mixing takes place in the pump.

At the base of the cylinder sodium nitrate of a purity of 96% separates and at the upper part av pulp formed of gas-oil, ammonium chloride and the mother liquor overflows.

This pulp is collected in a vat, agitated, and treated with 300 kg. of 60% HNOQ. The agitation is stopped and the gas oil collected at the surface for use in a following operation. At the lower part ammonium chloride of 92% purity is obtained with acidic mother liquor at the intermediate layer. r

If the ammonium chloride is desired at a higher purity, it is passed into another cylinder in the same manner. The acid mother liquor is treated with the required quantity of NH: to produce after evaporation of kg. of water a composition corresponding to the original composition ready for a new operation.

' In the above example the homogenization of the mixture is effected in a pump but all other means already used for this purpose may be employed, especially violent agitation in a vat.

I claim:

1. A process for the separation of ammonium salts from their mixtures with other FLJILM niacal salts comprising placing the mixture of the salts to be separated in suspension in a liquid of a density lower than that of each of the nonammoniacal salts of the mixture and inactive to all of the salts of the mixture, pouring into the suspension of flotation liquid having a density lower than that of the suspension liquid and incompletely miscible therewith, agitating the mixture, allowing the agitated mixture to stand in a large body, collecting the pulp floating on the surface which contains the flotation liquid and the ammonium salts of the original mixture, separatingthe ammonium salts from the flotation liquid, collecting the non-ammoniacal salts at the lower portion of the body, and-separating them from the suspension liquid.

2. A process according to claim 1, in which the hydrogen ion concentration of the suspension liquid is controlled to favor the formation and stability of the supernatant pulp.

3. A process for the separation of ammonium salts from their mixtures with other non-ammoniacal salts, comprising placing the mixture of the salts to be separated in suspension in a liquid of a density lower than that of each of the nonammoniacal salts of the mixture and inactive to all of the salts of the mixture, pouring into the suspension a flotation liquid having a density lower than that of the suspension liquid and incompletely miscible therewith, agitating the mixture, allowing the agitated mixture to stand in a large body, collecting the pulp floating on the surface which contains the flotation liquid and the ammonium salts of the original mixture, and modifying the hydrogen ion concentration of the pulp collected after the flotation to decompose the same and to separate the ammonium chloride, the flotation liquid and a certain quantity of the suspension liquid.

4. A process 'for the separation of ammonium salts from their mixtures with other non-ammoniacal salts, comprising placing the mixture of the salts to be separated in suspension in a liquid of a density lower than that of each of the nonammoniacal salts of the mixture and inactive to all of the salts of the mixture, pouring into the suspension a flotation liquid having a density lower than that of the suspension liquid and incompletely miscible therewith, agitating the mixture, allowing the agitated mixture'to stand in a large body, collecting the pulp floating on the surface which contains the flotation liquid and the ammonium salts of the original mixture, modifying the hydrogen ion concentration of the pulp collected after the flotation to decompose the same and to separate the ammonium chloride,

the flotation liquid and a certain quantity of the acid suspension liquid, collecting the suspension liquid after separation of the ammonium chloride and the flotation liquid, and modifying the hydrogen ion concentration of the suspension liquid to give it the same pH value of the original suspension liquid.

LOUIS ANDRES. 

